1. Field of Invention
The invention relates to a navigation system and a route guidance data storage program.
2. Description of Related Art
There are many kinds of conventional navigation apparatuses, wherein a present position of the vehicle is detected by GPS (Global Positioning System), a vehicle bearing is based on the vehicle's rotational angular speed (traverse angle) measured by a gyrosensor, cartographic data is read from a data storage unit, a map is drawn on a screen in a display unit; and therewith the present position of the vehicle, the vehicle bearing, and an area around the present position of the vehicle are displayed onto the map. The resulting map helps a user of the vehicle to travel along unfamiliar roads.
In the conventional navigation apparatus, selection of the destination and definition of a search criterion triggers route search from the present position to the destination. A searched route is presented to the user in at least one of two ways. It is displayed onto a search route view page on the screen, or outputted vocally from a voice output unit. Such presentation helps the user to travel along the searched route.
Some conventional navigation apparatuses have a communication unit to receive traffic information, including traffic congestion information. The traffic information received by the communication unit can be displayed onto the map.
Other conventional navigation apparatuses can be connected to an information center over communication networks. Such network-connectable navigation apparatus feature the following processes. When the user inputs his or her desired departure point and destination point from his or her personal computer before taking a drive, a route search data file kept in the information center is accessed and, proper route search data is readout from the information center. At the same time, the information center obtains the traffic information from an outside source. Then, the information center carries out a route search that is based on the inputted departure point, the inputted destination point, and the obtained traffic information. Finishing the route search, the information center prepares route guidance data consisting of voice output data, route data that visually represents the searched route or the like. Then, the prepared route guidance data is transmitted to the user's personal computer. In the user's personal computer, the route guidance data is downloaded onto a hard disk.
In the previously-described case of the network-connectable navigation apparatus, the information center is designed to store time-series statistical data derived from past traffic information, especially, past traffic congestion information. This allows the information center to search an optimal route based on not only the present traffic information but also the time-series statistical data.
Further, in the previously-described case of the network-connectable navigation apparatus, the route guidance data downloaded on the hard disk in the personal computer can be copied into, for example, a memory card. When loaded with the memory card, the navigation apparatus reads out the route guidance data from the card and then presents such route guidance data to the user, helping the user to travel along unfamiliar routes.